This invention relates to a hydrocracking process and a catalyst for use therein. More particularly, it relates to a hydrocracking catalyst of improved activity, selectivity, and stability for producing middle distillates from heavy gas oils and the like under hydrocracking conditions.
Petroleum refiners often produce desirable products such as turbine fuel, diesel fuel, and other middle distillate products by hydrocracking a heavy gas oil, i.e., a hydrocarbon fraction having a boiling point range between about 700.degree. F. and 1050.degree. F. Hydrocracking is accomplished by contacting the heavy gas oil at an elevated temperature and pressure in the presence of hydrogen and a suitable hydrocracking catalyst so as to yield a middle distillate fraction boiling in the 300.degree. to 700.degree. F. range and containing the desired turbine and diesel fuels.
The three main catalytic properties by which the performance of a hydrocracking catalyst for producing middle distillate products is evaluated are activity, selectivity, and stability. Activity may be determined by comparing the temperature at which various catalysts must be utilized under otherwise constant hydrocracking conditions with the same feedstock so as to produce a given percentage (usually 60%) of products boiling below 700.degree. F. The lower the activity temperature for a given catalyst, the more active such a catalyst is in relation to a catalyst of higher activity temperature. Selectivity of hydrocracking catalysts may be determined during the foregoing described activity test and is measured as that percentage fraction of the 700.degree. F.-minus product boiling in the range of middle distillate or midbarrel products, i.e., 300.degree. to 700.degree. F. Stability is a measure of how well a catalyst maintains its activity over an extended time period when treating a given hydrocarbon feedstock under the conditions of the activity test. Stability is generally measured in terms of the change in temperature required per day to maintain a 60% or other given conversion.
As could be expected, the aim of the art is to provide a catalyst having at once the highest possible activity, selectivity, and stability. Catalysts usually utilized for hydrocracking comprise a Group VIII metal component, most often cobalt or nickel sulfides, in combination with a Group VIB metal component, most often molybdenum or tungsten sulfides, supported on a refractory oxide. For given proportions of Group VIII and Group VIB metal components, the activity, selectivity, and stability of a catalyst change dramatically with different supports. Support materials comprising crystalline aluminosilicate zeolites, such as Zeolite Y in the hydrogen form, generally provide high activity but low selectivity, whereas support materials consisting essentially of refractory oxides, such as alumina, magnesia, and silica-alumina, generally have relatively poor activity but high selectivity.
The object of the present invention, therefore, is to provide a hydrocracking catalyst having superior overall catalytic properties for hydrocracking hydrocarbons. More specifically, it is an object of the invention to provide a catalyst having superior overall activity, selectivity, and stability for hydrocracking in comparison to prior art catalysts. It is a further object to provide a hydrocracking process for converting gas oils and the like to middle distillate products. It is a further object to provide a support or carrier material useful with a hydrogenation component as a catalyst for hydrogenating and/or hydrocracking hydrocarbons. These and other objects and advantages will become more apparent in light of the following description of the invention.